Large diameter femoral heads offer increased range of motion and reduced risk of dislocation. However, their use in total hip arthroplasty has historically been limited by their correlation with increased polyethylene wear. The improved wear resistance of highly crosslinked UHWMPE has led a number of clinicians to transition from implanting traditionally popular sizes (28mm and 32 mm) to implanting 36 mm heads. Desire to further increase stability and range of motion has spurred interest in even larger sizes (> 36 mm). While the long-term clinical ramifications are unknown, in-vivo measurements of highly crosslinked UHMWPE liners indicate increases in head diameter are associated with increased volumetric wear [1]. The goal of this study was to determine if this increase in wear could be negated by using femoral heads with a ceramic surface, such as oxidized Zr-2.5Nb (OxZr), rather than CoCrMo (CoCr). Specifically, wear of 10 Mrad crosslinked UHMWPE (XLPE) against 36 mm CoCr and 44 mm OxZr heads was compared. Ram-extruded GUR 1050 UHMWPE was crosslinked by gamma irradiation to 10 Mrad, remelted, and machined into acetabular liners. Liners were sterilized using vaporized hydrogen peroxide and tested against either 36 mm CoCr or 44 mm OxZr (OXINIUM(tm)) heads (n=3). All implants were manufactured by Smith & Nephew (Memphis, TN). Testing was conducted on a hip simulator (AMTI, Watertown, MA) as previously described [2]. The 4000N peak load (4 time body weight for a 102 kg/225 lb patient) and 1.15 Hz frequency used are based upon data obtained from an instrumented implant during fast walking/jogging and have previously been shown to generate measurable XLPE wear [2,3]. Lubricant was a serum (Alpha Calf Fraction, HyClone Laboratories, Logan, UT) solution that was replaced once per week [2]. Liners were weighed at least once every million cycles (Mcycle) over the duration of testing (∼ 5 Mcycle). Loaded soak controls were used to correct for fluid absorption. Single factor ANOVA was used to compare groups (a = 0.05).Introduction
Materials and Methods
The most common bearing couple used in total knee arthroplasty (TKA) is ultra-high molecular weight polyethylene (UHMWPE) articulating against a CoCrMo alloy femoral component. Although this couple has demonstrated good clinical results, UHMWPE wear has been identified as one of the principal causes for long-term failure of total knee joint replacements1 indicating a need for improvements in TKA bearings technology. The wear resistance of UHMWPE can be improved by radiation crosslinking; however, in order to get the full benefit of this improved wear resistance, an abrasion resistant ceramic counterface is necessary.2 Since the radiation crosslinking degrades mechanical properties, it is also important to have an optimized radiation dose and subsequent processing. The purpose of this study was to evaluate the long-term wear performance of VERILAST Technology comprising two advanced bearing technologies, abrasion resistant OXINIUM femoral components (OxZr)3-4 and wear/strength optimized 7.5 Mrad crosslinked polyethylene (7.5-XLPE).5 Three component assemblies of LEGION(tm) cruciate retaining (CR) OxZr femoral components, 7.5-XLPE tibial inserts were tested on an AMTI knee simulator under displacement control at 1 Hz frequency as described previously.2 The tibial inserts were manufactured from compression molded GUR 1020 UHMWPE, radiation crosslinked to 7.5 Mrad dose, remelted to extinguish free radicals, and sterilized by EtO. The wear test was conducted for 45 Mcycle, which was considered to be a conservative estimate for the amount of cycles that would occur during 30 years of typical in-vivo use based on the relationship between patient age and the number of loading cycles as reported in the literature.6-8Introduction
Materials and Methods
Perioperative delirium (POD) is not uncommon in orthopaedics. We prospectively followed one hundred and thirty-two arthroplasty patients and thirty hip fracture patients using POD as the outcome. Patient interviews, chart reviews and application of the Mini Mental Status Exam (MMSE) were used to identify risk factors for POD. Having two or more risk factors or low scores on the MMSE was predictive of POD. Development of POD significantly increased patient length of stay. It may be possible to identify “at risk” patients for POD and intervene preoperatively so as to improve outcomes. The purpose of this study was to identify risk factors for delirium in arthroplasty and hip fracture patients among routinely collected data. Risk factors for perioperative delirium (POD) in arthroplasty and hip fracture patients can be identified. In elderly hip fracture patients, cognitive impairment as measured by preoperative performance on the Mini Mental Status Exam (MMSE), appears to have a strong association with development of POD. As delirium is associated with adverse outcomes, it may be possible to target interventions to reduce the incidence of POD in patients who are at greatest risk, and potentially improve outcomes. The incidence of POD was lower in elective orthopaedic patients (13.6%) than in fracture patients (40%). Among elective arthroplasty patients, having two or more risk factors was associated with an eight-time increase in the incidence of delirium and increased length of stay (9.5 days versus six days). Length of stay was considerably higher in hip fracture patients with two or more risk factors (18.9 days vs. 9.9). A low score on the MMSE was the best predictor of developing POD in hip fracture patients. We recorded age, sensory impairment, functional status, history of previous POD, and use of alcohol or benzodiazepines, in one hundred and thirty-two hip or knee arthroplasty patients, and thirty elderly patients awaiting surgery for hip fracture. All patients completed the MMSE preoperatively. Delirium was documented prospectively by the Confusion Assessment Method. POD has an adverse effect on outcomes and is not uncommon in orthopaedics. Risk factors have been identified that could be used for preoperative screening and intervention.
